1. Field of the Invention
The invention is generally directed to methods and apparatus for quenching a hot gaseous stream. The invention is more specifically directed to methods and apparatus for quenching the pyrolysis product from a pyrolysis furnace.
2. Description of Related Art
Assignee""s olefins plant was the first gas oil steam cracker plant in which it was recognized that wetting of the quench tube wall is essential in order to keep the quench tube from fouling because of coke deposits. One of Assignee""s designs, using a spray nozzle to introduce the quench oil for cooling the hot pyrolysis gas exiting the radiant section, did not work because of the difficulties in keeping the walls completely wetted. Previous nozzle configurations included an external quench ring encircling the quench tube for distributing quench oil between three nozzles arranged 120 degrees apart around the quench tube. This design created excessive thermal stress on the quench ring. Later, it was modified into three separate quench nozzles, all sharing one quench oil supply line, which required a flow restriction in each nozzle to ensure good distribution of quench oil.
The restriction orifices and smaller sized nozzles in the prior multi-nozzle oil injection quench tubes were frequently plugged by coke particles present in the quench oil. When this occurred, the quench oil flow wetting the quench tube wall was interrupted and this led to incomplete wetting of the quench tube wall. Coke would form and grow on the dry spot of the quench tube wall and would eventually plug the quench tube. When this occurred, the entire furnace had to be shutdown for cleaning. Even without problems with the injection nozzles, the quench tube was subject to coke formation and plugging at the moving boundary between wetted and dry walls near the oil inlets.
A quench nozzle design introduces quench oil tangentially into the quench tube and cools the hot gaseous pyrolysis products coming out of the hot radiant tubes in a pyrolysis furnace (e.g., in ethylene manufacture). Besides cooling the hot gases, the quench oil introduced into the quench tube by this nozzle design keeps the wall of the quench tube wetted, which is necessary to prevent coke deposition on the quench tube. The nozzle has one quench oil entry, thus eliminating the need for any restriction orifice which would be required to evenly distribute quench oil flows between several nozzles. Also, the one-nozzle oil introduction has a larger diameter than that required if more than one nozzle were employed in this service. The replacement of multiple nozzles (and restriction orifices) with a single larger diameter nozzle eliminates plugging problems caused by coke particles present in the quench oil. The quench tube walls are maintained wetted by the use of an internal ring with a specially-tapered leading edge and an abrupt terminal end which serves to prevent the quench oil/gas interface from moving axially back and forth in the quench tube, and thereby eliminating coke formation.